In general, a conventional heat pipe comprises a capillary structure primarily including sintered powder, grooves, meshes or fine fibers, and the capillary structure is usually distributed on the whole or a part of an internal cavity wall of the heat pipe. As to the heat pipe with the capillary structure distributed on the whole internal cavity wall, a circular core rod is generally adopted, so that the manufacturing process is simple and easy. On the other hand, the thin heat pipe has insufficient evaporation space after the heat pipe is manufactured and pressed flatly and limitation on portability, so that it is necessary to increase the effective capillary thickness. Even if the thickness is reduced below 2 mm, the thermal conductivity of the heat pipe will be very poor. To improve the insufficient liquid and vapor space of the thin heat pipe, capillary structures distributed partially on the internal cavity wall as disclosed in US Pat. Application Nos. 20070006993, 20100266864, and 20120118537 are introduced, wherein the insufficient capillary reflow and vaporization space of the pressed heat pipe can be improved by using a non-circular core rod and filling powder on a single side or both sides of the core rod, but the vapor in the cavity of the heat pipe is still in direct contact with the liquid channel, and thus the capillary reflow capability is reduced significantly, and the performance of the thin heat pipe requires improvements.
To achieve the effect of separating the liquid and vapor in the heat pipe or using plural capillary structures to separate the vapor from the liquid channel, the heat pipe structures as disclosed in U.S. Pat. Nos. 7,316,264 and 8,453,718 comprise a grooved pipe with a sintered metal powder, or a grooved pipe with a mesh to achieve the effect of separating liquid and vapor in the cavity of the heat pipe. Wherein, the vapor and the liquid channel are mainly separated by the sintered powder or mesh structure, the exterior of the capillary structure and the groove of the internal cavity wall are used as the liquid reflow channel, and the space from the interior of the capillary structure to the cavity of the heat is used as the vapor channel. Such arrangements can improve the performance of the heat pipe effectively. As to the heat pipe with the capillary structures distributed on the whole of the internal cavity wall, it is relatively difficult to manufacture a thin heat pipe with a plurality of capillary structures. As disclosed in U.S. Pat. Application Nos. 20120111540, 20100319882, and 20130168054, the structures having a non-circular core rod and powder filled on a single side or both sides of the core rod together with the groove formed on a part of the internal cavity wall are used to achieve the effect of separating liquid and vapor in the cavity of the heat pipe and improve the performance of the thin heat pipe. Due to the plurality of capillary structures, the thickness of the thin heat pipe is still limited by the capillary structures, and a thin heat pipe cannot be manufactured easily. In U.S. Pat. Application Nos. 20120111540, 20100319882, and 20130168054, although the effect of the heat pipe is still to separate the liquid and gas, yet the liquid channel acts as a grooved structure between the sintered metal powder and the upper and lower internal walls, and the vapor channel is formed on both sides of the cavity of the heat pipe. Now, the sintered metal powder does not have the direct separating effect, but it acts as a secondary liquid channel which is affected by vapor directly, so as to offset the capillary reflow capability of the sintered structure and affect the performance of the thin heat pipe.
Since the amount of heat generated by electronic products becomes increasingly larger, and the electronic products are designed and developed with high portability, thin and light, 4K video, 4G transmission, high add-on function, and multi-tasking computation, the conventional thin heat pipe can no longer meet the high heat and flux requirements anymore.
In view of the drawbacks of the prior art, it is a main subject of the present invention to provide a feasible design to improve the capillary structure of a flat heat pipe with a better performance and overcome the aforementioned drawbacks of the prior art.